90 240sx rough idle after warmup, stutter between shifts

[Imakulate]

OK. I tried searching new and archived posts but couldnt come up with anything.. When I first start her up she goes right into a nice idle that I set at around 800-900. It have left it idling for about 10 minutes and no problems. I have a gutted cat (came like that when I purchased car), along with no EGR or AC compressor, lines, etc.. the problem is that when I drive her for about 10-15 miles, after shes good and warmed up, the car starts dropping to real low RPMs between shifts and I have to give it some gas and let it get past some stuttering until it finally jumps up into the higher RPMs and then shift. I know shes running lean by the smell of gas alone. the car has about 155k miles on it and is obviously a SOHC. I think that maybe the gutted cat has something to do with it. I think I read something about how the ECU adjusts the full mix for the cat and when you remove it the mixture gets thrown off or something...

anyway The car cost me 1100 and seemed like a good deal at the time but now I'm worried its just going to get worse the more I drive it. Knowing 240s share many of the same problems and all of us have experienced a multitude of problems, I;m sure this has happened to alot of us. So any help is appreciated. Thanks.

[rogoman]

After the motor is fully warmed up, the smell of gas in the exhaust indicates an overly rich condition. This may be due to a bad temperature sensor that the ECU uses input from.

[Imakulate]

any idea as to which sensor it could be or how I can find out?

[Imakulate]

well its definitely getting worse. Now after its been warmed up and I turn her off she won't start back up for a little, like the motors flooded. So I am up to any suggestions....